Data transmission

ABSTRACT

A device for data transmission by light has a waveguide doped with a fluorescent material. A light source is arranged to provide modulated light to enter the waveguide through an upper surface, the fluorescent material being responsive to the modulated light to emit light omnidirectionally. The emitted light is guided towards and emitted through end surfaces of the waveguide.

The present invention relates to data transmission by means ofelectromagnetic radiation and is applicable by way of example toposition encoders.

Data transmission by means of electromagnetic radiation, e.g. light, isa useful technique in cases where data has to be transferred across agap and/or between relatively movable parts. As a special case, adigital position encoder modulates the radiation with a code dependentupon the relative positions of two parts, one of which carries codeelements which are able to modulate the radiation, e.g. by reflection ortransmissivity.

According to a first aspect of the invention there is provided a devicefor data transmission by electromagnetic radiation comprising a memberconstituting a waveguide, means for providing pulsed or modulatedradiation comprising a first frequency to enter the waveguide and meansfor detecting radiation at a second frequency at an end surface of thewaveguide, the member having within it fluorescent material responsiveto radiation at the first frequency to emit radiation at the secondfrequency, the emitted radiation being guided by the waveguide to theend surface.

According to a second aspect of the invention there is provided aposition detector for detecting the relative positions of two partscomprising a data transmission device according to the above firstaspect.

In one embodiment the means for providing modulated radiation comprisesa plurality of portions relatively opaque to radiation at the firstfrequency and disposed between the waveguide and the source of radiationso that the radiation will be modulated by the pattern of said portions.

According to a third aspect of the invention there is provided aninfusion pump transmission comprising a position detector according tothe above second aspect, one of said parts being means for operating asyringe infusion pump plunger and the second being means arranged to beconnected to the syringe infusion pump body.

According to a fourth aspect of the invention, there is provided adevice for data transmission by electromagnetic radiation comprising awaveguide for the radiation, the waveguide having two, opposed, majorsurfaces, one of which provides an input for the radiation to thewaveguide, an end or edge surface of the waveguide providing for outputof radiation, there being source means of radiation for supplyingradiation to said one major surface, detector means responsive to thedirected radiation emitted from said end or edge surface, and means inthe waveguide and responsive to input radiation for directing radiationtowards the end or edge surface, that radiation being guided between themajor surfaces.

In one example, the waveguide may be of a type containing fluorescentmaterial having a maximum of absorption in the region of the frequencyof the input radiation and a maximum of emission at a frequency to whichthe detector means is responsive.

There may be a plurality of elements relatively opaque to said pulsedradiation between the source and the waveguide, said elements beingarranged according to an n-bit digital position code. The source meansmay comprise n individual sources for illuminating the respective bitsin sequence, the device being arranged so that a single detector can beused to receive a series of bits defining the relative position of thesource means and the code.

A waveguide doped or loaded with fluorescent material is readilyobtainable at low cost. By virtue of its ability to emit light at aspecific frequency when subjected to light at another, it proves to havea relatively good output light intensity compared with the incidentintensity, i.e. good transfer properties.

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made, by way of example,to the accompanying drawings, in which:

FIG. 1 illustrates a data transmission device having a waveguide;

FIG. 2 illustrates a linear position detector;

FIG. 3 illustrates the drive and detector circuits for the detector ofFIG. 2;

FIG. 4 is a perspective view of a syringe infusion pump transmissionincorporating a position detector according to FIGS. 2 and 3; and

FIG. 5 illustrates a rotary data transmitter.

FIG. 1 shows a data transmission device comprising a light waveguidestructure 1 with light incident on its upper surface 2, the light beinggenerated by a pulsed source 3. According to the material properties ofthe waveguide, some of the light will be reflected from the surface,some will be transmitted through the waveguide, exiting through thelower surface 4, and the remainder will be either absorbed by thematerial or will be scattered within the material and be guided therebyto exit through the four side edges 5. If the material is relativelytransparent, the majority of light will pass straight through thematerial. If, however, the material is opaque, most of the light will beabsorbed. In either case, very little of the light will be emittedthrough the edges.

Consider, however, a waveguide constructed using a relativelytransparent material such as glass or plastics, which is doped with afluorescent dye or compound. An example of such a material is a plasticssheet manufactured by Bayer AG under the trade name LISA, beingpolycarbonate doped with flourescent material. This exhibits a peakabsorption at an approximate wavelength of 521 nm and a correspondingpeak fluorescent emission at approximately 595 nm.

If light of a wavelength at or near the peak absorption wavelength isincident on the upper surface 2, a high proportion of it will beabsorbed, with the subsequent emission of light at or near 595 nm. Thislight is emitted omni-directionally and a major portion of it will hitthe upper and lower surfaces at an angle greater than the critical anglethus being confined between these surfaces. Thus light will be guidedout towards the side edges 5 and will be emitted therefrom. Aphotodetector 6 having a peak response at approximately 595 nm, andbeing positioned at one of the edges, will respond to the emitted lightby producing corresponding electrical signals. It will be clear that byusing such a device, a modulated light signal impinging on the uppersurface 2 can be converted into an electrical signal at the output ofthe photodetector 6. This is accomplished even if there is a gap betweensource 3 and waveguide 1 and or if there is relative motion between thetwo. It will be apparent that for a given fluorescent emission producedwithin the waveguide the intensity of light emitted can be increased bydecreasing the surface area of the edges through which light is emitted.

FIG. 2 shows one possible application of the device, illustrating aposition encoder 7 for determining the absolute position of a body 8with respect to a fixed stage 9. Attached to a lower surface of the bodyis a row of 8 light emitting devices 10a to h, in this case these beinglight emitting diodes (LEDs), arranged so as to emit light in agenerally downward direction. The LEDs are connected to electronicdriving circuit 11, which may be either mounted on the body, on thestage, or elsewhere. The driving circuit is designed to allow the LEDsto be illuminated in a controlled sequential manner and to control theamount of drive current used. The voltage across and/or the currentthrough the LEDs may be monitored by a microprocessor of the pump inorder to detect their malfunction. Affixed to the stage 9 is a detector12 comprising a waveguide 13 constructed using the fluorescently dopedmaterial described above, and which is generally rectangular in shapethough tapering inwardly at one end to form a narrow throat 14. Abuttedagainst the throat is a photodetector 15 which may be a photo diode orsimilar such device, and which is connected to a suitable electronicdetection circuit 16 for detecting the electrical output from thephotodetector. The detector may be a detector sensitive to red orinfrared and proves to have adequate sensitivity at 595 nm. A detectorwith a peak sensitivity nearer to 595 nm could, of course, be used inpreference.

Printed on the upper surface of the waveguide 13 are a series of 8 bitcode sequences 17 arranged sequentially along the length of thewaveguide. The width W of the sequences is equal to or greater than thewidth of the LEDs attached to the body 8. Each code sequence consists ofa series 17a to h of eight interspersed optically transparent/opticallyopaque segments or bits arranged in a linear row across the width of theguide. The encode is shielded from ambient light.

The operation of the linear position encoder 7 will now be described.The body 8 is located directly above and parallel to the stage 9, sothat the LED array lies fractionally above the surface of the waveguide,the LEDs lying over respective bits of one code sequence. If the body 8is designed to move from right to left as seen in FIG. 2, the arraywould be arranged such that, at the rightmost position of the body, thearray would lie directly above the rightmost code sequence on the uppersurface of the waveguide.

The LEDs are chosen to have a peak emission wavelength at or near thepeak excitation wavelength (521 nm) of the fluorescent material of thewaveguide.

The driving circuit 11 is operated so as to illuminate LED 10a for agiven time. This LED is then turned off and LED 10b is illuminated forthe same time period. Similarly LEDs 10c to h are illuminated in turn,with the cycle repeating over regular intervals.

A proportion of the light emitted by each LED is coupled into the guidethrough its upper surface if the illuminated diode lies over atransparent bit of the code. If, however, the LED lies over an opaquebit, no significant amount of light will enter the guide. Light enteringthe guide will tend to excite the fluorescent material, resulting inemission at or near 595 nm.

As described above, the majority of the emitted light will travelthrough the waveguide exiting through the side edges. Some of the lightwill exit through the throat 14 where it will enter the photodetector15. This will result in an electrical pulse being generated by thephotodetector 15 of duration corresponding to the duration of theemitted light. As each of the LEDs is illuminated, a series of pulseswill result corresponding to the code sequence directly below the LEDarray.

FIG. 3 illustrates one possible configuration of the detection circuit16 and the drive circuit 11. The latter has a counter 26 which isclocked by clock 25 to count from 0 to 7, reset, and repeat, the outputbeing a three bit binary word. This word is decoded by a 3-to-8 linedecoder 27 which addresses LED driver 28 and which in turn drives theselected LED.

The detection circuit 16 has a serial to parallel converter 29 connectedto receive the pulses generated by the photodetector 15. The output fromconverter 29 is an 8 bit word which is stored by a latch 30. Both theconverter and the latch are synchronised by the clock 25 to capture the8 bits present between illumination of first LED 10a and the turning offof last LED 10h. An output of the counter 26, produced every 8 counts,controls the converter and the latch to inform them of the start andfinish of each 8 bit word. Once a word has been received and stored inthe latch, a decoder 31 is used to convert the code into a positionvalue, e.g. as a binary number, which is a measure of the absoluteposition of the body with respect to the stage and which can then bedisplayed on a display output 32.

It is to be noted that many of the functions of the above circuit may becarried out by the microprocessor and memory used to control otherfunctions of the pump.

The resolution of this system is determined by the width W of the codesequences. In the preferred embodiment W is 0.5 mm with the total lengthof the coded upper surface being 10 centimeters, i.e. 200 codesequences. If a unique code is required for each position, then eightbit code sequences and eight LEDs are required.

Code sequences could be selected in many ways. However, manyarrangements may give erroneous results when the array is positionedmidway between two neighbouring sequences. This problem is overcome byusing a code such as a Gray code, where only one bit of the code changesbetween neighbouring sequences.

FIG. 4 illustrates the use of a position encoder in a syringe infusionpump transmission. Such a transmission is disclosed in U.K. Patent No. 2224 444. The transmission comprises a fixed plate 33 in which isrotatably mounted a leadscrew 34. The leadscrew can be moved axiallythrough the fixed plate 33, by means of a motor 36 and associated gears,to drive a carriage mechanism 37. The carriage mechanism comprises adrive plate 38, a sleeve 39 and a body 40 connected in sequence. Thedrive plate 38 is arranged to drive the plunger of a syringe infusionpump, not shown, whose body portion is fixed relative to the fixed plate33. The body 40 has an arm 41, on the lower surface of which are mountedthe LEDs 10a to h. Beneath the arm and spaced apart from the LEDs is thedetector 12 which is fixed relative to the syringe body and fixed plate.

The motor 36 may have its own high resolution encoder 42 but the encoderdescribed with reference to FIG. 2 provides an absolute measurement onthe plunger itself. Its resolution may be relatively low but,nevertheless, it provides data of sufficient accuracy to enable the datafrom the motor encoder to be checked and corrected if necessary, thusgiving more reliable information.

In an alternative embodiment of a position encoder according to thepresent invention, the source array, the waveguide and the detector arestationary and the code sequences are attached to the plunger whichmoves the code sequences between the array and waveguide.

A further embodiment has the detector 15 positioned centrally as showndotted in FIG. 2 in order to minimise light travel paths. Moreover thesurfaces of the waveguide may be angled so as to improve the guiding ofthe light to the detector 15.

FIG. 5 shows a second embodiment of a position encoder according to thepresent invention. A rotating shaft or device 18 has one or more, e.g.three, LEDs 19 in a disk positioned on one end surface 20. The or eachLED is driven by electronic pulse drive means located within the device(not shown). A disk 21 constructed using the fluorescently dopedplastics material described above is attached to the LED disk 20 torotate with the device 18. A photodiode 22 or similar photodetector islocated adjacent the disk periphery 23 with only a small gap between itslight input surface 24 and the periphery 23 of the disk.

The LED drive means transmits pulses to the or each LED, which pulsesare output as a series of light pulses. As described above, the outputwavelength of the LED light is selected to be at or near the fluorescentexcitation peak of the fluorescent material, resulting in the emissionof light within the disk 21 at the emission peak of the material.

This light will travel radially outwards towards the periphery 23, fromwhere it will be uniformly radiated. Detector 22 will receive the lightand generate corresponding pulsed electrical signals.

It is clear that, no matter what the relative angular position of thedevice 18 and the disk 21, signals can be transmitted between the deviceand the detector.

Whilst this embodiment includes only one LED disk 20 and one detectordisk 21, a plurality of such pairs of disks could be positioned on thedevice 18, each having a separate detector 22 and light source 19,allowing simultaneous transmission of several signals.

Moreover, the or each disk 23 might alternatively be stationary ratherthan rotate with the device 18. In another alternative, the disk 21might rotate whilst the device 18 is fixed.

This data transmission principle is equally useful for applicationsinvolving a limited range of linear motion.

Such a device can also be designed as a rotary encoder. The LED disk mayhave a radial series of LEDs to rotate with device 18, whilst the disk21 might be fixed and have a plurality of radially extending Gray codesequences.

In order to increase the signal to noise ratios of any one of the abovedescribed embodiments, unused surfaces i.e. those not directly receivinglight from the input source and those not directly emitting light to thedetector, may be mirror coated to retain within the waveguide lightradiation which would otherwise be emitted therefrom.

I claim:
 1. A device for data transmission by electromagnetic radiation,between relatively movable first and second parts, of a plurality ofdigital bit values forming a digital multi-bit word, the devicecomprising:a member constituting a waveguide for electromagneticradiation and having a radiation input surface and an end outputsurface; a plurality of sequentially operable means for providingrespective pulsed beams of radiation comprising a first frequency toenter the waveguide at the radiation input surface; means for receivingradiation at a second frequency at the end output surface of thewaveguide; the member having within it fluorescent material responsiveto radiation at the first frequency to emit at the second frequencyradiation guided by the waveguide to the end output surface; and meansfor modulating the beams according to the respective bit values of themulti-bit word; whereby the radiation at the second frequency at the endoutput surface constitutes a serial digital stream of the respective bitvalues.
 2. A device as claimed in claim 1 wherein the fluorescentmaterial has a maximum of absorption in the region of the firstfrequency.
 3. A device as claimed in claim 2 wherein the frequency ofmaximum absorption is 521 nm.
 4. A device as claimed in claim 2 whereinthe fluorescent material has a maximum of emission at the secondfrequency.
 5. A device as claimed in claim 4 wherein the frequency ofmaximum emission is 595 nm.
 6. A device as claimed in claim 1 whereinthe waveguide is a planar waveguide having two opposed major surfaceswhich act as guide surfaces for the emitted radiation.
 7. A device asclaimed in claim 6 wherein the means for providing radiation is arrangedto provide it through one of the major surfaces.
 8. A device as claimedin claim 1 wherein said end surface is substantially perpendicular to aguide axis of the waveguide.
 9. A device as claimed in claim 1, whereinthe waveguide has at least one surface coated with a reflective coatingwherein light confinement within the waveguide is improved.
 10. A deviceas claimed in claim 1 wherein the said end surface of the waveguide isat a narrow end of a throat portion formed by at least one taperingsidewall of the waveguide, wherein light defined from any one of theproviding means may be guided to the same portion of that narrow end.11. A device as claimed in claim 1 wherein the means for receivingradiation comprises a single detector.
 12. A position detector fordetecting relative position and comprising two parts which arerelatively movable in a direction of relative motion and means fordetecting the relative position of said parts comprising:a memberconstituting a waveguide for electromagnetic radiation and having aradiation input surface and an end output surface; a plurality ofsequentially operable means attached to a first of the two parts forproviding respective pulsed beams of radiation comprising a firstfrequency to enter the waveguide at the radiation input surface as asequence of beams extending at an angle to the direction of relativemotion of the two parts; means for receiving radiation at a secondfrequency at the end output surface of the waveguide; the member havingwithin it fluorescent material responsive to radiation at the firstfrequency to emit at the second frequency radiation guided by thewaveguide to the end output surface; means interposed between the memberand the means for providing radiation for modulating the beams; themodulating means having a plurality of beam modulating strips whichfollow one another in a sequence which extends in the direction ofrelative motion of the two parts, the strips defining respective anddistinct multi-bit words in that each strip is effective to modulate thebeams according to respective bit values of the associated multi-bitwords; and means attaching the modulating means to a second of the twoparts so as to interpose a different strip between the member and themeans for providing radiation according to the relative position of themember and the means for providing radiation; whereby the radiation atthe second frequency at the end output surface constitutes a serialdigital stream of the respective bit values of a digital word definingan absolute position.
 13. A position detector as claimed in claim 12wherein said modulating means comprises a plurality of elementsrelatively opaque to radiation at the first frequency positioned betweenthe means for providing radiation and the waveguide, the elements beingarranged in an n-bit code.
 14. A position detector as claimed in claim13, comprising n of said selectively operable means for illuminatingrespective bits in the code.
 15. A position detector as claimed in claim14 comprising a plurality of the said n-bit codes arranged sequentiallyin the direction of relative motion of the two parts.
 16. A positiondetector as claimed in claim 15 wherein the plurality of n-bit codes arearranged sequentially as a Gray code.
 17. A position detector as claimedin claim 13 wherein the elements forming the codes are on a surface ofthe waveguide and the detecting means are arranged to be fixed relativeto the first of the parts and the plurality of means for providingradiation are arranged to be fixed relative to the second of the parts.18. A position detector as claimed in claim 13 wherein the waveguide,detecting means and plurality of means for providing radiation arearranged to be fixed relative to said first of the parts and theelements forming the codes are arranged to be fixed relative to thesecond of the parts.
 19. A position detector as claimed in claim 12wherein the parts are arranged for relative linear motion.
 20. Aposition detector as claimed in claim 12 wherein the parts are arrangedfor relative rotary motion.
 21. A syringe infusion pump transmissioncomprising a first part, being means for operating a syringe infusionpump plunger, a second part, being means arranged to be connected to asyringe pump body with the parts being relative movable, and a positiondetector comprising:a member constituting a waveguide and having an endsurface; a plurality of sequentially operable means attached to thefirst part for providing respective pulsed beams of radiation comprisinga first frequency to enter the waveguide as a sequence of beamsextending substantially at right angles to the direction of relativemotion of the parts; means for receiving radiation at a second frequencyat the end surface of the waveguide; the member having within itfluorescent material responsive to radiation at the first frequency toemit at the second frequency radiation guided by the waveguide to theend surface; means interposed between the member and the means forproviding radiation for modulating the beams; the modulating meanshaving a plurality of beam modulating strips which follow one another ina sequence which extends in the direction of relative motion of the twoparts, the strips defining respective and distinct multi-bit words inthat each strip is effective to modulate the beams according torespective bit values of the associated multi-bit words; and meansattaching the modulating means to the second part so as to interpose adifferent strip between the member and the means for providing radiationaccording to the relative position of the member and the means forproviding radiation; whereby the radiation at the second frequency atthe end output surface constitutes a serial digital stream of therespective bit values of a digital word defining an absolute position.